(1) Field of the Invention
The present invention relates to methods and devices for energy conversion.
(2) Description of Related Art
The presented invention is a further development of the previous invention according to U.S. Pat. No. 6,841,891, 2005, based on the theoretical principles given in ISBN 3-8288-1255-4, Luchinskiy, A., Renewable energy sources: Complex of technical solutions, Tectum—Wissenschaftsverlag, Marburg, 2002.
The methods of so-called “direct” and “not-direct” conversion of heat energy into electric energy are known. By “direct” methods the heat energy is converted into the electric energy directly and immediate. To the “direct” methods of energy conversion belong for example thermophotovoltaical energy conversion or energy conversion through thermoelectrical Seebeck-phenomenon. By “not-direct” methods the heat energy is converted firstly in an other form of energy, in particular in a mechanic energy, and only finally—in the electric energy. So, there is an “energy conversion chain” in the “not-direct” methods. To the “not-direct” methods of energy conversion belongs a method, which one is executed in all traditional “fossil” heat power stations, as well as in the nuclear power stations. Namely, the heat energy is firstly converted in the mechanic energy, and after that the mechanic energy is converted in the electric energy. To the “not-direct” methods belong also the methods, which are executed in the sun “tower”-type power stations, sun groove (“parabolic trough”-type) power stations, in the Stirling-method, and in our method according to U.S. Pat. No. 6,841,891. A detailed consideration of the above-mentioned methods is presented below.
On actual state of technology the “not-direct” methods of energy conversion are more efficient, than the “direct” methods. Therefore, for example, for the industrial producing of electricity the traditional heat power stations with a mechanic-electrical Faraday-generator are used, instead of a pile of thermophotovoltaic plates, placed in a Furnace.
Furthermore in details. A generally known method of sun energy conversion, namely photovoltaic, is known wherein a sun radiation energy or a light energy can be converted in the electric energy through an absorption of photons in a semiconductor. This method provides a possibility to generate electric energy in devices, which have no mechanically moving parts, no burning of fuels, and no consumption of working materials.
Photovoltaic is efficient and effective in respect to other methods in the cases, where one need a local generation of relatively low electric energy amounts under the condition of relatively low supply of energy in the form of sun light (or light from other sources). For example to use in calculators, parking-automats, for some home appliances with very low electric power, etc. Nevertheless this method is not effective for generation of high power electricity (for example in power stations) already because of the fundamental physical principles, in the reason that only a very narrow frequency range of sun radiation is used, which one leads to the releasing of electrons in a semiconductor.
Therefore the shortcomings of this a.m. method is a relatively low efficiency and high costs, as well as the large dimensions of a converter in respect to the produced electric power. Besides, there is a physical limit of efficiency, which one cannot be exceeded in no case, because the executing this method devices are converting in the electric energy only the energy of photons, which are absorbed in the material of the semiconductor. I.e. only a narrow part of range from all spectrum of the sun radiation can be used. There is also a physical limit for the intensity of coming sun radiation, which one can be usefully used, because the electric output power does not increases more if some definite level of radiation intensity is already attained. Besides, there are numerous inconveniences because of the necessity to protect permanently the large valuable working surfaces from dirt and mechanic damages, wherein the sun light have to fall down on these surfaces direct and unimpeded.
For the utilization of industrial heat wastes the photovoltaic methods are self-evidently not applicable.
A method for energy conversion, named thermophotovoltaic, is known, by which one an infrared radiation is converted in the electric energy by a semiconductor. Considerable attention and investments have been given to this direction of investigations, but there is no industrial using of this method yet. The reason for interest is not only a prospect to use a sun radiation spectrum more efficiently (i.e. not only a visible, but also an infrared part of sun radiation spectrum). As a main prospect of this method could be a possibility to utilize the industrial heat wastes. This last application is not less, but probably even more important one, than the using of sun energy, because presently at least 30-40% of all produced energy has been lost in the form of industrial heat wastes. And besides these energy wastes are acting as heat pollutions.
Nevertheless the extremely high temperatures of the heat source (at least 1000 degrees centigrade) are required for the thermophotovoltaic methods. This temperature is attained by burning of fuels (in the experimental heat generators a gas propane is normally used as a fuel). In output it is approximately 5% efficiency reached, in respect to the input energy of infrared radiation. In respect to an all used energy, i.e. in respect to the all energy, which one was released by burning of fuel, the efficiency is even less.
This method is presently still in the stage of experimental investigations. Besides, there are still no results, which could provide a guarantee that a possibility of industrial usage will be ever reached.
As better developed, in respect to the practical applicability, methods one can mention the thermodynamic methods of conversion of sun energy and heat energy, in particular of the energy of industrial heat wastes, in the electric energy or in other useful forms of energy. Methods for energy conversion are known, over many years, wherein a sun radiation energy is converted in an electric energy by heat solar power stations. In these methods the sun radiation energy is converted in a heat energy of some working body, and this heat energy is converted by some heat machine in a mechanic energy. The produced this way energy is converted then in an electric energy by some mechanic-electric converter.
The common disadvantages of these methods are big energy losses, as well as a necessity to convert a sun radiation energy or heat energy first in a mechanic energy, which fact reduces an efficiency and presupposes an existence of mechanically moving parts in the devices, by which devices these methods are executed.
Furthermore, the “tower”-type and “parabolic trough”-type solar power stations (“Turmkraftwerke” and “Rinnenkraftwerke” have the following disadvantages, which determine the limits of their applicability: first, very high (caused already by the construction principle) intermediate losses because of scattering.
Secondly, also caused by the construction principle, very large dimensions of the system and large total surface area, which one is occupied by a such system. With other words, one can use these systems effectively only in desert regions with the continuously high sun radiation from a cloudless sky, wherein the used plot of land must be cheap to make reasonable an energy supply of a small settlement or of a small industrial object by a big power station, which one occupies a correspondent large land surface area.
And besides, the small local systems are impossible because of construction principles.
On the present state of technology, as a most acceptable for a mass consumption method, among all thermodynamic methods, the Stirling-method is known. The proposed and disclosed in this description technical solution can be set off mainly against the Stirling-method.
The already existing Stirling-method:
Makes it possible mainly the constructions of small, but as well also of middle-large energy converters. (Besides, for comparison, the “tower”-type and “parabolic trough”-type solar power stations, can exist only as large systems; and on the other hand, the proposed in this description our method provides the construction of all “spectrum” of energy converters: both low power systems, which can use already small temperature differentials, both the middle- and high power systems).
Stirling-method has the following advantages, which make it presently the most acceptable energy conversion method in a sun power energetics:
1) Stirling-method provides a possibility to use already small temperature differences. (Some demonstration motors are known, which works from the temperature difference between human hands and environment air).
2) Stirling-method has a theoretically high efficiency of conversion of heat energy, in a mechanic energy.
In the practice however the additional losses occur by conversion in an electric energy. Furthermore, the work processes happen relatively slowly because of the necessary compression and expansion of the working gas, which slowness causes the next losses.
The deciding shortcomings of this method have to be described below more detailed, because these disadvantages are not directly highlighted obvious way in the technical literature about the Stirling-method. Therefore it remains unclear, why such efficient method does not replace all other methods in practice.
Firstly, a significantly low output power is caused already by the construction of Stirling-converter, because in the base of the working processes lay the slow processes of heat expansion and compression of the gas under the temperature, which one is much higher, then a boiling temperature of the working gas.
Secondly, concerning the efficiency: there are normally 3 following misunderstandings in the descriptions, which, as a rule, are not taken into account.
1) The efficiency (EF) is, as it is known, a ratio of useful work Auseful to the expended work Aexpended: EF=Auseful/Aexpended.
Or also the efficiency is a ratio of useful power Nuseful to the expended power Nexpended: EF=Nuseful/Nexpended.
To put this another way, EF=Auseful/Aexpended=Auseful×t/Aexpended×t=Nuseful/Nexpended, where t is time.
I.e. time t cancels out, and an efficiency of a system in this calculation does not depend on a time period, during which this work was executed. This way by this calculation a very high efficiency can be obtained also for devices, which have a negligibly small (i.e. practically useless) power.
2) If it is written, that an efficiency of a Stirling-motor can attain 50%, one normally means the following:
Firstly the case in point is the efficiency of conversion of a heat energy of some heater in a mechanic energy of Stirling-motor, wherein the further losses during the conversion of this mechanic energy in the electric energy are not taken into account.
Secondly, the following hypothetic situation is assumed: Stirling-motor get it's heat energy from a thermo-insulated heater, which one have an infinite heat capacity, and then this Stirling-motor passes the heat rests to a cooler, which one also has the same properties as well. But in fact it is not so. If an energy comes from the sun, simultaneously a backscattering (re-irradiation) in the space takes place. If an energy comes from an outer heat source, the coming heat energy will not “wait” in a contact zone with a Stirling-motor cylinder all the time, as long as the Stirling-motor working gas will absorb, during it's slow expansion, all the coming heat energy. This a.m. heat energy will be dissipated as well through re-irradiation, thermal conduction and convection. This way the factual losses are high, and the factual efficiency is low, if the process takes a lot of time, and consequently an output power of the converter is also low. Therefore a real efficiency of a Stirling motor is not very high in reality.
3) In order for the diagram-picture, which one describes a work of a sun-driven Stirling-motor, not to differ essentially from the ideal diagram of the Carnot-cycle (Carnot-process), and, consequently, the Stirling-motor to have a high efficiency, this Stirling-motor must work slowly. Slow work means a low output power. This way the requirement to have a high efficiency and the requirement to have a high output power are physically incompatible for a Stirling-motor, and they make contradictory demands on it's construction execution.
It is necessary also to make one note here concerning a parameter, which one at all characterizes a working effectiveness of a sun energy converter. Sun energy in a form of sun radiation is “free of charge”. There are no expenses for producing, processing and transport of this energy. The not-used part of this energy does not transform itself in harmful pollutants, which are coming in environment; in the opposite, the used part of this energy is taken off from the natural circulation of the energy in the environment. Therefore in fact an efficiency on its own is not a main parameter, which one characterizes a sun energy converter, and it is not an end in itself to achieve a high efficiency.
One much more important parameter is a ratio of output power of a sun energy converter to it's dimensions (in particular a ratio Noutput/S, where Noutput is the output power of the converter, and S is the occupied by converter surface area. This parameter is similar to the parameter of efficiency, but these two parameters are not identical. As it was shown above, a converter with a high efficiency can have a negligibly low output power.
For these reasons, i.e. because of the in fact relative low output power and low efficiency, the Stirling-method is not used widely in actual practice.
Our previous method according to U.S. Pat. No. 6,841,891 makes it possible to use for an effective energy conversion also also the heat sources, which provide small temperature differences. Besides, this method provides a possibility to increase the power and efficiency of the energy conversion through reducing of the necessary for conversion time and reducing of the intermediate energy losses (s. description of the U.S. Pat. No. 6,841,891, Int. Kl.7 F02G 1/00, publication year 2005).
The presented there our earlier solutions made it possible to increase an efficiency of the method and to increase a ratio of output power of the converter, which one executes this method, to it's dimensions. It was attained because of maximal usage of a sun radiation energy (on frequency spectrum and intensity), because of minimizing of the energy conversion intermediate loses, and because of removing of necessity to convert a sun radiation energy in a mechanic energy of some mechanic details in an intervening phase. This way a possibility was attained, to execute a producing of electric energy with a high output power and high efficiency in relation to the converter dimensions. It is attained such way, that the proposed design principle of an energy converter is based on the physical bases of the already known heat pipe systems. This converter converts a gas flow energy of a heat pipe working body directly in an other form of energy, finally in an electric energy.
High quickness of energy absorption and energy conversion by a working body, and consequently low intermediate energy losses, more high output power and efficiency by a same temperature difference are attained such way, that instead of the slow processes of heat extension and heat compression of a gas, the method is based on the physical phenomena, which take place by evaporation (vaporization) and condensation of a working liquid on porous structures.
Besides, the devices, which execute the proposed method, must not contain the mechanically moving details of construction. And besides, the concerning invention has a more wide spectrum of applications in comparison with the existing solar- and heat-into electricity converters. It takes place because this method can be embodied both in the low power devices, which can use already the small temperature differentials, and in the middle- and high power devices.
This way these solutions make it possible to increase an output power of a converter also in the cases, when this converter converts heat energy by low temperature differences, and consequently it has low efficiency. It was also shown by the author, that an efficiency and an output power are not the unambiguously correlated parameters. For example, a converter with a high efficiency can, in the same time, have a negligibly low output power. And vice versa, a converter with a low efficiency can, in the same time, have an essentially high output power (ISBN 3-8288-1255-4, Luchinskiy, A., Renewable energy sources: Complex of technical solutions, Tectum—Wissenschaftsverlag, Marburg, 2002 (germ); Luchinskiy, A., Relationship among efficiency and output power of heat energy converters, ArXiv: General Physics/0409017; September 2004.